Bipolar plate for fuel cells, fuel cell stack with such bipolar plates as well as vehicle with such a fuel cell stack

Abstract

The invention relates to a flow field plate for a fuel cell, which has an anode plate (30) with an anode side (31) and a coolant side (32), a first structure (33) being formed on the anode side (31) to form an anode flow field (34), and a cathode plate (40) with a cathode side (41) and a coolant side (42), a second structure (43) being formed on the cathode side (41) to form a cathode flow field (44), wherein structure elements (51) are arranged between the anode plate (30) and the cathode plate (40) to form a coolant flow field (50), said structure elements being in contact with the coolant sides (32, 42) of the anode plate (30) and the cathode plate (40). Said flow field plate has an optimised pressure distribution in a fuel cell stack (100) and greater stability than the prior art because, according to the invention, the structural elements consist of an elastic material. The invention further relates to a fuel cell stack and a vehicle.

Description

[0001] The invention relates to a bipolar plate for a fuel cell comprising an anode plate with an anode side and a coolant side, wherein a first structure for forming an anode flux field is formed on the anode side; a cathode plate with a cathode side and a coolant side, wherein a second structure for forming a cathode flux field is formed on the cathode side; wherein structural elements are arranged between the anode plate and the cathode plate for forming a coolant flux field, and these structural elements are contacted by the coolant sides of the anode plate and the cathode plate. The invention further relates to a fuel cell stack with such bipolar plates and to a vehicle comprising such a fuel cell stack.

[0002] Fuel cells utilize the chemical reaction of a fuel with oxygen to produce water, thereby generating electrical energy. As a core component, fuel cells contain the membrane electrode assembly (MEA), which consists of an ion-conducting (usually proton-conducting) membrane and a catalytic electrode (anode and cathode) positioned on either side of the membrane. These electrodes typically comprise supported precious metals, especially platinum. Additionally, gas diffusion layers (GDLs) can be arranged on both sides of the MEA, on the electrodes facing away from the membrane. A fuel cell is generally formed by a stack of multiple MEAs, whose electrical voltages are additive.Bipolar plates (also called flow field or separator plates) are typically arranged between the individual membrane electrode assemblies. These plates ensure the supply of the operating media, i.e., the reactants, to the individual cells and usually also serve for cooling. Furthermore, the bipolar plates provide an electrically conductive contact with the membrane electrode assemblies.

[0003] In the operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen (H₂) or a hydrogen-containing gas mixture, is supplied to the anode via an open flux field on the anode side of the bipolar plate. There, electrochemical oxidation of H₂ to protons (H⁺) takes place, releasing electrons (H₂ → 2 H⁺ + 2 e⁻). The protons are transported (either water-bound or anhydrous) from the anode compartment to the cathode compartment via the electrolyte or the membrane, which separates the reaction compartments gas-tight and provides electrical insulation. The electrons produced at the anode are then transferred to the cathode via an electrical conductor. Oxygen or an oxygen-containing gas mixture (for example, air) is supplied to the cathode via an open flux field on the cathode side of the bipolar plate as the cathode operating medium, so that a reduction of O 2 to O 2-< takes place with the uptake of electrons (1 / 2 O 2 + 2 e -< → O 2-< ).At the same time, in the cathode compartment, the oxygen anions react with the protons transported across the membrane to form water (O 2-< + 2 H 2+< → H 2 O).

[0004] The fuel cell stack is supplied with its operating media, i.e., the anode operating gas (e.g., hydrogen), the cathode operating gas (e.g., air), and the coolant, via main supply channels that run the entire length of the stack and from which the operating media are fed to the individual cells via the bipolar plates. At least two such main supply channels are provided for each operating medium: one for supplying and one for discharging the respective operating medium.

[0005] Bipolar plates typically consist of two interconnected half-plates, each structured on both sides. On the opposite sides, the structures are required for the transport of the operating fluids, while on the opposite sides, they are required for the transport of coolant. The half-plates must be precisely matched to each other, as three separate transport paths must be provided using just two half-plates. This leads to further constraints that reduce the flexibility of the bipolar plate design. In typical designs, the half-plates of known bipolar plates are profiled, with the profiles interlocking or nested within each other.

[0006] The fuel cell stack typically has end plates at its opposite ends, which are connected to each other by clamping devices as part of a clamping system. These clamping devices transmit tensile forces that pull the end plates together and compress the individual cells arranged between them, pressing them against each other. Compression springs are also part of the clamping system to distribute the load evenly across the stack and prevent damage.

[0007] From DE 10 2004 016 494 A1 a fuel cell arrangement with stacked fuel cells is known which has elastic structures within the fuel cell stack.

[0008] WO 2004 / 112178 A2 discloses an electrochemical arrangement in which the elastic distribution structure is guided in a plane.

[0009] WO 2010 / 054647 A2 discloses a fuel cell module that can be put into operation without bipolar plates.

[0010] US patent 2005 / 0106444 A1 discloses a fuel cell stack with two corrugated partitions for cooling, which have a flat and elastic plate between them.

[0011] The invention is based on the objective of providing a bipolar plate which at least partially eliminates the disadvantages of a bipolar plate that it has in conjunction with pressure springs.

[0012] This problem is solved by a bipolar plate, a fuel cell stack and a vehicle with such a fuel cell stack having the features of the independent claims.

[0013] The bipolar plate comprises an anode plate with an anode side and a coolant side, wherein a first structure for forming an anode flux field is formed on one anode side. The bipolar plate further comprises a cathode plate with a cathode side and a coolant side, wherein a second structure for forming a cathode flux field is formed on the cathode side. Structural elements are arranged between the anode plate and the cathode plate to form a coolant flux field, and these structural elements contact the coolant sides of the anode plate and the cathode plate. According to the invention, the structural elements are made of an elastic material.

[0014] These structural elements serve as embedded springs in a fuel cell stack with the bipolar plates according to the invention, among other things to optimize compression while simultaneously increasing structural robustness.

[0015] Furthermore, this allows the stacking height of the fuel cell stack to be reduced compared to the prior art, as the compression springs typically used are no longer necessary. These prior art compression springs also do not provide good control of the contact pressure on the active surface of the bipolar plate, and the resulting uneven stack compaction can lead to plate breakage. This is avoided by the bipolar plate according to the invention. In addition, weight can be saved by eliminating the compression springs. Bending of the end plate is also minimized. A particularly advantageous aspect is that the effects of GDL / MEA ingress can be minimized.

[0016] Furthermore, cost reductions in plate production can be achieved, for example by eliminating compression springs and by using the Form-In-Place (FIP) process for mass production.

[0017] The bipolar plate according to the invention, apart from the structural elements, preferably consists of a conductive material, preferably a carbon-based material, particularly preferably graphite or a composite material of graphite and carbon. The use of metal is also provided for.

[0018] The structural elements provided according to the invention preferably consist of an elastic conductive polymer that is stable in the temperature range of fuel cell operation, wherein preferably at least one structural element is conductive. Silicones or siloxanes are preferably used, with polydimethylsiloxane being particularly preferred.

[0019] The polymer preferably has an electrical conductivity of > 100 S / cm. An electrical resistance is preferably 0.0008 W / cm and the bulk modulus is preferably 5 MPa.

[0020] The structural elements are arranged at a distance from each other between the anode plate and the cathode plate, so that the coolant can flow through the coolant flow field of the bipolar plate with the lowest possible pressure loss.

[0021] The structural elements are designed in a columnar shape, preferably with a constant cross-section over the entire length of the individual structural element or with a cross-section that varies over the length, for example with a reduced cross-section in the middle of the structural elements.

[0022] The structural elements can have cross-sectional areas of different sizes distributed across the surface of the bipolar plate in order to meet different requirements for spring force in different areas of the bipolar plate.

[0023] Preferably, the structural elements have a rectangular or square cross-section, allowing for very simple manufacturing. Furthermore, round or oval cross-sections with one or two axes of symmetry are also possible.

[0024] In particularly preferred embodiments of the bipolar plate according to the invention, the structuring of the anode plate and the cathode plate is designed such that at least the contact surface of the structural elements on the respective opposite sides of the anode plate and cathode plate is covered by the structuring in order to distribute the pressure over the entire stack height. Thus, the first structuring of the anode side and the second structuring of the cathode plate, as well as the structural elements in the stacking direction of the bipolar plates, are arranged directly one above the other. Advantageously, this prevents damage to the bipolar plate.

[0025] Further spatial configurations of the anode plate and cathode plate can easily be implemented to optimize flow conditions. A configuration equivalent to that of the structural elements is preferred.

[0026] The invention also allows for the mixing of structural elements with different cross-sections.

[0027] The structural elements can be arranged regularly or irregularly within the coolant flow field, forming flow zones, in order to avoid pressure losses and to apply the necessary spring force as needed. Preferably, the structural elements, and optionally the structuring, form a grid pattern when arranged regularly.

[0028] The structural elements are preferably fixed to at least the anode plate or the cathode plate, for example by gluing, whereby one-sided fixing can facilitate the assembly of the bipolar plates and is generally sufficient. Gluing to the cathode plate carrying the oxidizing agent is preferred.

[0029] According to the invention, the structural elements are arranged and provided on a carrier plate. This carrier plate preferably consists of the same material as the structural elements and, according to the invention, is manufactured integrally with the structural elements.

[0030] The support plate can be arranged either against the anode plate or the cathode plate. This advantageous design allows for a significantly simplified assembly of the bipolar plate according to the invention. In this embodiment as well, bonding to at least the anode plate and the cathode plate can be carried out analogously to the individual structural elements.

[0031] Apart from the specifications described above, the flow fields of the anode plate and the cathode plate, as well as the coolant flow field, can be individually designed independently of each other.

[0032] Another aspect of the invention relates to a fuel cell stack comprising a stack of alternately arranged membrane electrode arrangements and bipolar plates according to the invention between two end plates.

[0033] Furthermore, the invention relates to a vehicle comprising a fuel cell system with a fuel cell stack according to the invention. The vehicle is preferably an electric vehicle in which electrical energy generated by the fuel cell system is used to supply an electric traction motor and / or a traction battery.

[0034] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0035] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0036] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Figure 1 is a schematic representation of a fuel cell stack; Figure 2 is a perspective view from above showing a detail of a bipolar plate not covered by the invention; Figure 3 is a perspective view from below showing a detail of the bipolar plate according to Figure 2 Figure 4 shows a sectional view detailing the bipolar plate. Figures 2 and 3Figure 5 shows a perspective view detail of a cathode plate with structural elements; Figure 6 shows a sectional view detail of a bipolar plate according to a second embodiment according to the invention; Figure 7 shows a perspective view detail of a cathode plate with structural elements arranged on a support plate; Figure 8 shows a perspective view detail of a cathode plate with structural elements arranged on a support plate according to a second embodiment; Figure 9 shows a top view of structural elements with an oval cross-section on a support plate; and Figure 10 shows a top view of structural elements with an oval cross-section on a support plate according to a second embodiment.

[0037] Figure 1Figure 1 shows a schematic representation of a fuel cell stack, designated as 100, according to the present invention. The fuel cell stack 100 is part of a vehicle (not shown), in particular an electric vehicle, which has an electric traction motor that is supplied with electrical energy by the fuel cell stack 100. The fuel cell stack 100 comprises a plurality of membrane electrode assemblies 10 and bipolar plates 12 arranged alternately at their flat sides (stacked). Thus, several stacked individual cells 11 together form the fuel cell stack 100, whereby both one of the individual cells 11 and the fuel cell stack 100 can generally be referred to as a fuel cell. The fuel cell stack 100 has end plates 18 on both sides.Between the bipolar plates 12 and the respective membrane electrode assemblies 10, anode and cathode compartments (not shown) are arranged, which are delimited by circumferential seals 20. Among other things, to establish the sealing function of the seals 20, the fuel cell stack 100 is compressed (pressed) together in the stacking direction S by means of a clamping system.

[0038] The clamping system comprises an external clamping device 22, as well as elastic structural elements (not visible here) arranged in the coolant area of ​​the bipolar plates 12. These are described in more detail below.

[0039] To generate an external tension, which is transferred to the structural elements in the fuel cell stack 100, elongated tension bodies 24 of the external clamping devices 22 transmit tensile forces between the two end plates 18, so that the end plates 18 are pulled towards each other by means of the tension bodies 24. For this purpose, the tension bodies 24 extend in a stacking direction S of the fuel cell stack 100.

[0040] Figures 2 to 4 The figures show a bipolar plate 12 not encompassed by the invention in different views. Each figure shows a detail of the bipolar plate 12.

[0041] The bipolar plate 12 comprises two individual plates: an anode plate 30 and a cathode plate 40. The anode plate 30 has an anode side 31 and a coolant side 32, which faces the cathode plate 40. The cathode plate 40 has a cathode side 41 and a coolant side 42, which faces the anode plate 30. To form a coolant flow field 50, elastic structural elements 51 are arranged between the anode plate 30 and the cathode plate 40, on coolant sides 32 and 42, respectively, and contact the anode plate 30 and the cathode plate 40. The structural elements 51 are column-shaped and have a square cross-section. They are uniformly distributed and thus form flow paths 52 in the form of a grid, through which a coolant can flow in the longitudinal and transverse directions with respect to a principal axis of the bipolar plate 12.

[0042] On the anode side 31 and cathode side 41 facing away from the coolant flow field 50, a first structuring 33 and a second structuring 43, respectively, are provided. Both are designed analogously to the structural elements 51 of the coolant flow field 50 and form an anode flow field 34 and a cathode flow field 44. That is, they are column-shaped with a square cross-section. Furthermore, they form flow paths 35, 45 for the two reaction media, which are located in the Figures 2 to 4 in the stacking direction S are identical to the structural elements 51.

[0043] In Figure 5 An example will also be given according to the Figures 2 to 4 shown, however with the difference that the anode plate 30 is not shown.

[0044] The differing sizes of the structural elements 51 in the center of the cathode plate 40, compared to those at the edges, are solely due to the section shown and have no technical significance. Of course, it is fundamentally possible to dimension the structural elements 51 differently and distribute them unevenly. To simplify the assembly of the bipolar plate 12, the structural elements 51 are fixed or glued at least on the coolant side 42 of the cathode plate 40.

[0045] Figure 6Figure 1 shows a section detail of a bipolar plate 12 according to a second embodiment of the invention. In this embodiment, the structural elements 51 are integrally formed with a carrier plate 53, the flat side of which rests on the coolant side 42 of the cathode plate 40. The anode plate 30 (not shown) is applied to the cathode plate 40 after the carrier plate 53 with the structural elements 51 has been arranged, thus completing the bipolar plate 12. The use of this carrier plate 53 significantly simplifies the assembly of the bipolar plate 12. Bonding of the carrier plate 53 or the structural elements 51 is also possible in this variant.

[0046] The other variant, in which the side of the support plate 53, which carries the structural elements 51, rests on the coolant side 42 of the cathode plate 40, is in Figure 8 shown. This variant otherwise corresponds to the one in Figure 7 shown.

[0047] The Figure 9 and 10 Each shows a carrier plate 53 with structural elements 51 applied to it, which have an oval cross-section with two axes of symmetry ( Figure 9 ) and an oval cross-section with an axis of symmetry ( Figure 10 These embodiments serve to optimize the flow characteristics of a coolant. These cross-sections can also be selected as the first structuring 33 and / or second structuring 43. Unless explicitly stated otherwise, the following applies equally to all embodiments. Reference symbol list

[0048] 100 Fuel cell stack 10 Membrane electrode assembly 11 Single cell 12 Bipolar plate 18 End plate 20 Seal 21 Spring system 22 Tensioning device 24 Elongated pulley 30 Anode plate 31 Anode side 32 Coolant side 33 First structuring 34 Anode flow field 35 Flow path 40 Cathode plate 41 Cathode side 42 Coolant side 43 Second structuring 44 Cathode flow field 45 Flow path 50 Coolant flow field 51 Structural elements 52 Flow path 53 Support plate S Stack direction

Claims

1. Bipolar plate (12) for a fuel cell comprising: an anode plate (30) having an anode side (31) and a coolant side (32), wherein a first structuring (33) is formed at the anode side (31) in order to form an anode flux field (34), and a cathode plate (40) having a cathode side (41) and a coolant side (42), wherein a second structuring (43) is formed at the cathode side (41) in order to form a cathode flux field (44); wherein structural elements (51) which are contacted by the coolant sides (32, 42) of the anode plate (30) and the cathode plate (40) are arranged between the anode plate (30) and the cathode plate (40) in order to form a coolant flux field (50), wherein the structural elements (51) comprise a resilient material, characterized in that the structural elements (51) are formed on a carrier plate (53) which is arranged bearing either on the anode plate (30) or on the cathode plate (40), wherein the carrier plate (53) can be or is fixed to the anode plate (30) or the cathode plate (40), and in that the carrier plate (53) is produced integrally with the structural elements (51).

2. Bipolar plate (12) according to claim 1, characterized in that the anode plate (30) and the cathode plate (40) consist of metal or a conductive, carbon-based material, preferably graphite or a composite material comprising graphite and carbon.

3. Bipolar plate (12) according to claim 1 or 2, characterized in that the structural elements (51) consist of a resilient polymer, wherein at least one structural element is conductive.

4. Bipolar plate (12) according to any one of the preceding claims, characterized in that the structural elements (51) are column-like and preferably have a rectangular or oval cross-section and are arranged with spacing from each other.

5. Bipolar plate (12) according to any one of the preceding claims, characterized in that the first structuring (33) of the anode plate (30) and the second structuring (43) of the cathode plate (40) are positioned one above the other in the stacking direction (S) and overlap each other at least partially with the cross-sectional surface-area of the structural elements (51).

6. Bipolar plate (12) according to any one of the preceding claims, characterized in that the structural elements (51) are arranged in a regular or irregular manner with flow paths (52) being formed.

7. Bipolar plate (12) according to any one of the preceding claims, characterized in that the structurings (33, 43) of the anode plate (30) and / or the cathode plate (40) are arranged in a column-like manner.

8. Fuel cell stack (100) comprising a stack between two end plates (18) of alternately arranged membrane / electrode arrangements (10) and bipolar plates (12) according to any one of claims 1 to 7.

9. Vehicle having a fuel cell stack (100) according to claim 8.

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